The aide, Brent Furer, has had repeated brushes with the law dating back to the 1990s, an ABC News investigation has found. Yet Furer has continued to receive his taxpayer-financed senate staff salary in Washington, even as court records show he remains wanted on an open warrant in Baton Rouge stemming from an unresolved misdemeanor DWI charge.

Reached at Vitter's senate office, Furer declined to comment, saying he was "too swamped" with the office's response to the Gulf of Mexico oil spill. He did not respond to questions emailed by ABC News. Vitter, a 49-year-old first-term Republican who is up for reelection in November, also declined to comment when approached in front of his senate office building Tuesday.

A Vitter spokesman acknowledged the senator had concerns about the 2008 arrest, in which Furer was accused of holding his ex-girlfriend against her will for 90 minutes, threatening to kill her, placing his hand over her mouth, and cutting her in the hand and neck.

"After the January 2008 incident, he was told to leave the office pending the court's determination of what happened," spokesman Joel DiGrado said in an emailed response to questions from ABC News.

DiGrado said that after Furer was sentenced, Vitter imposed "further significant disciplinary action" in consultation with the congressional employment legal office, though he would not elaborate on what that entailed. He said the senator hired Furer because of the aide's military service during the first Gulf War.

Furer's presence on Vitter's staff is just the latest instance in which the senator's publicly stated views on women's issues appear to clash with his actions. In 2007, Vitter issued a public apology after acknowledging being a client of the so-called D.C. Madam. The 2008 allegations against Vitter's longtime aide are described in chilling detail in court papers.